Photosensitive materials, such as photoresists, are light sensitive materials, typically polymer-based, that may be patterned using photolithography and used to generate structural features ranging in size from tens of nanometers to centimeters. In photolithography, light is used to transfer a geometric pattern from a photomask to a photoresist film on a substrate, and parts of the film are then selectively removed in a developer, thereby defining the transferred pattern. The technology has proven successful for patterning photoresists on flat substrates and has been widely applied to the fabrication of microelectronic and MEMS devices.
In general, depositing and patterning polymers on non-planar substrates—such as etched, curved, or porous surfaces—remains difficult. Conventional methods of applying polymers to surfaces, including spin-coating and spraying, may result in coatings of non-uniform thicknesses when non-flat substrates are used. Significant challenges exist in adapting photolithography to three-dimension multiple level substrates and/or curved substrates due to its reliance on projection optics and the limited depth of focus.